Re: String of numbers into to array of numbers

Mark Space <>
Sun, 28 Sep 2008 22:56:09 -0700
bH wrote:

Hi All,
Here are 2 attempts to get it correct.

I might be a bit confused as to what you are trying to do. Does all
this just change strings into ints? You seem to be doing a lot of work
here when you could just be calling an existing String method.

I did a version last week, thinking I understood what problem statement
was. All I did was call "getBytes()". If I understand correctly, that
one call replaces most of your first program.

Rather than use Roedy's routine, I just wrote my own. Here's my
attempt. It's not very good. It has no Java doc, I use number literals
rather than declaring constants, and I just read the Wikipedia entry and
implemented their example. A real implementation would need to code
carefully to the RFCs and would need a lot more unit testing.

However, if you read the main method, you can see that my test is quite
short. I use the four strings that Wikipedia provides encodings for,
and check them myself for correctness. To turn strings into arrays of
bytes, I just call getBytes() as I mentioned.

If I understand the problem correctly, you are trying to implement
"decode" as below. (Mine's not done.) Is that true?

package local;

public class Base64

     private static final String alphabet64 =

     // Base64 is final and non-instantiable only.
     private Base64()

     public static String encode( byte[] b )
         StringBuilder sb = new StringBuilder(
b.length*4/3+b.length/48*4+6 );
         for( int i = 0; i<b.length; )
             // 1
             int base = (b[i]>>>2)&0x3F;
             sb.append( alphabet64.charAt( base ) );
             if( i+1<b.length )
                 // 2
                 base = (b[i]<<4)&0x30|(b[i+1]>>>4)&0xF;
                 sb.append( alphabet64.charAt( base ) );
                 if( i+2<b.length )
                     // 3
                     base = (b[i+1]<<2)&0x3C|(b[i+2]>>>6)&0x3;
                     sb.append( alphabet64.charAt( base ) );
                     // 4
                     base = b[i+2]&0x3F;
                     sb.append( alphabet64.charAt( base ) );
                     // 3, no third byte
                     base = (b[i+1]<<2)&0x3C;
                     sb.append( alphabet64.charAt( base ) );
                     sb.append( "=" );
                 // 2, no second byte
                 base = (b[i]<<4)&0x30;
                 sb.append( alphabet64.charAt( base ) );
                 sb.append( "==" );
             i+= 3;
// if( i % 48 == 0 ) {
// sb.append( '\n' );
// }
         return sb.toString();

     public static byte[] decode( String s )
         return new byte[1];

     public static void main( String... args )

         String test[] =
             "Man is distinguished, not only by his reason"
         for( String testString : test )
             String enc = encode( testString.getBytes() );
             System.out.println( "The string:\n"+testString+
                     "\n\nis encoded as:\n"+enc+"\n" );

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